1. Field of the Invention
This invention relates to an apparatus for processing a digital signal such as a digital signal in MIDI (Musical Instrument Digital Interface) format designed to control electronic musical instruments.
2. Description of the Prior Art
Conventional MIDI format for a digital signal is designed to control electronic musical instruments. In a known MIDI-based music control system, MIDI signals are transmitted between various electronic musical instruments and a keyboard so that the musical instruments can be driven and controlled by operating the single keyboard.
Japanese published unexamined patent application 62-146470 discloses a digital information recording and reproducing system. In the system of Japanese patent application 62-146470, 8-bit MIDI code words representative of control information such as an interval, a scale, and a length of a note (sound) is recorded on a magnetic tape by a tape recorder of the helical scan type. When the MIDI words are reproduced from the magnetic tape, a start bit and a stop bit are added to each of the reproduced MIDI words to compose a 10-bit MIDI signal designed to drive and control electronic musical instruments.
A compact disk (CD) is an excellent recording medium for storing a large amount of digitized information. Since CD signal format and MIDI signal format are significantly different from each other, it is generally difficult to directly record MIDI words on a compact disk. For example, a MIDI word has 8 bits while a usable part of a CD subcode has 6 bits. In addition, the bit rate of the MIDI system is 31,250 bps (bit per second) while the bit rate of the CD subcode is 28,800.
A conventional MIDI system lacks the ability to cope with the occurrence of an uncorrectable MIDI data error or a sudden interruption of the transmission of a MIDI signal. Therefore, in such a case, some of electronic musical instruments of the MIDI system tend to continue the generation of notes (sounds), and the note generation control is disabled.